Microphone apparatus for telephone and other circuits.



Q. MAJORANA. MICROPHONE APPARATUS FOR TELEPHONE AND OTHER CIRCUITS.

APPLIOATION II LED JULY 7, 1906.

Patented Oct. 27, 1908.

' from an orifice flows through a certain dis- QUIRINO MAJORANA, OF ROME, ITALY.

MICROPHONE APPARATUS FOR TELEPHONE AND OTHER CIRCUITS.

Specification of Letters Patent.

Application filed July 7, 1906.

Patented Oct. 27, 1908.

Serial No. 325,106.

To all whom it may concern.

Be it known that I, QUiRINo MAJonANA, a subject of the King of Italy, residing at Rome, in Italy, have invented certain new and useful Improvements in or Relating to Microphone Apparatus for Telephone and Other Circuits, of which the following is a specifica tion.

The present invention relates to improvements in electro-hydrodynamic microphones for telephone and other sound-conveying systems, wherein a liquid jet is employed in the circuit for the purpose of reproducing the sounds transmitted by producing the very intensified variations of current in the circuit and therefore very intensified sounds.

The properties of liquid jets have been known for years, and many physicists have made them the object of their studies.

This invention, which is based upon the above phenomenon, relates to an improved form of microphone and is characterized by the fact that it enables telephonic currents to be obtained which are much stronger than those obtained with ordinary microphones. This invention contributes, therefore, to the solution of the problem of long distance telephoning through underground and submarine cables, over long iron wires, or, generally, over wires with great resistance.

According to the principle upon which this invention is based, a jetof liquid escaping tance which. is dependent on. the size of the orifice and on the pressure acting on the liquid in the vessel. Beyond that distance, it begins to break into drops which follow each other continuously and sometimes with a very high frequency. in this way such a frequency, under certain conditions, represents the vibration period proper of the jet. The existence of this period can be ascertained acoustically by letting the jet impinge, at the point where it begins to become reduced or to break, against an elastic diaphragm which in this way repeats a sound exactly corresponding to each period. Moreover the jet can be caused to vibrate in periods diil'ering to a considerable extent. When external mechanical vibrations (even if they do not have a character perceptible to the ear) strike the liquid jet, or rather the lower end of the water supply pipe, the. liquid thread shows periodical contractions l and swellings which are nearer to the outlet orifice than usual. Such reductions correspond exactly to the vibrations produced in the pipe from the outside, and the diaphragm against which the jet impinges, repeats the sounds corresponding to the said periods. This correspondence is the more exact, the nearer the diaphragm is to the outlet orifice, but in this case the sounds produced are weaker. At greater distances from the orifice the proper period of the jet begins to become mixed with the above-mentioned sounds, whereby theyare more or less impaired or neutralized. When the jet impinges against a flat surface which is nearly normal to it, a kind of liquid film is produced on the said plate or surface, the thickness of which varies in accordance with the vibrations of the jet.

In the above-described systems as hereto fore proposed, a jet of liquid issuing from a tube attached to a vibratory diaphragm has been projected upon a compound electrode connected in a telephone or other circuit, and consisting of a central conducting wire surrounded by a ring of insulating material and an outer conducting ringadapted to vary the resistance of the telephone circuit, but such arrangement has not been proved successful in practice owing to the vibrations not being sufficiently free and the required construction proportions and relation of the parts not being correctly understood.

The "present invention which utilizes the physical principles above referred to, en ables sounds of very great strength and purity to be produced.

The invention willbe now fully described with reference to the accompanying drawings which illustrate a number of forms or arrangements of apparatus according to this invention.

Figure 1 is a cross-sectional view of an apparatus constructed in accordance with this invention. Fig. 2 is a vertical section showing a slightly modified construction. Figs. 3 to 7 inclusive are detail sectional views showing different constructions and arrange- .ments of the horizontal diaphragm and contiguous parts seen in Fig. 1. Figs. 8 to 13 are detail sectional views showing different constructions and arrangements of the vertical diaphragm and contiguous parts seen in Fig. 2. Figs. 14 and 15 are sectional views of two different forms of collector.

Fig. 1 is a cross-section of a construction of an improved apparatus as applied in a telephone circuit. A speaking tube or transmitter A concentrates the sound waves coming from the outside on a horizontal elastic diaphragm B. Through the center of the latter passes a pipe C, the bottom opening of which is made in a special manner, and which is connected with another pipe D passing through the transmitter A. The pipe D is elastic only at the bottom and thus enables the diaphragm to effect vibrations freely which are transmitted to the liquid flowing through the pipes D and C. "he various methods of obtaining this partial elasticity will be hereinafter explained. The pipe D serves to guide the liquid jet E consisting of mercury or, still better, of water, rendered more conductive of electricity by the addition of an acid or a salt, to the shorter pipe C.

The liquid for the jet is supplied from any desired tank which is not shown in the draw ings. The level of the tank can be altered by any simple device which need not be described. The liquid jet flows smoothly for a certain distance, and then begins automatically to show periodic contractions with an oscillating period depending on the various elements which constitute the apparatus. As this has an injurious effect, the jet must be interrupted before these contractions take place. This is effected by means of an apparatus which may be called a collector and which will now be described.

The object of the collector is to effect the closing of an electric circuit in a variable manner. This variability corresponds to the amount of the contractions of the jet, which are caused by the sounds which cause the diaphragm B to vibrate. The collector is constituted by at least two cylindrical concentric conducting bodies F G made of some material, such as platinum, not affected by the liquid. The two conducting bodies F G are insulated from each other by means of some solid material H, such as glass, porcelain, enamel, vulcanized rubber, etc., and the upper surface of the three bodies in question (see lower part of Fig. 1) is made very smooth, so that the various parts present a smooth unbroken whole. The collector is supported by a vessel 1 which is provided with an outlet opening L. The liquid jet impinges exactly against the center of the upper surface of the collector and there forms a fine liquid film which electrically connects the two conducting bodies F and G. A circuit into which is switched a telephone M and an electric cell or battery N is connected to the conductor bodies F and G. In this electric circuit circulates a uniform current when no sound is made in front of the speaking tube A, and when consequently the jet of liquid does not experience any contractions or variation. When the liquid jet is electrolytic (water), there appears on the upper surface of the collector, in a striking man ner, an electrolysis of the liquid, which produces in the telephone a slight hissing sound which, however, does not affect the working of the apparatus. It is of great importance, when the liquid is electrolytic, to make the conducting parts of the collector at the top of large area.

The central conductor must be of sufficient diameter to freely transmit electric currents of great intensity while the width or thickness of the insulating ring H must be of the same order of dimensions as the liquid wave corresponding to the mean sound wave to be transmitted. It is possible to obtain currents of great intensity in this way and to render harmless the above-mentioned disturbance caused by the electrolysis.

When sounds coming from the outside strike the diaphragm B, the outlet tube is caused to vibrate, and consequently the jet E becomes reduced in a varying manner, so that the thickness of the liquid film forming on the collector continuously varies. The intensity of the telephonic current therefore varies, and reproduction of the sounds or words spoken in front of the tube A is thus obtained. It goes without saying that the telephone M instead of being switched directly into the circuit of the cell or battery N, can be switched together with a telephone line, into the secondary circuit of an induction coil, the primary coil of which occupies the present position of the telephone. The connection of the diaphragm with the bottom portion of the pipe D can also be made as shown in Fig. 2 in which the diaphragm B is vertical. In this case the pipe D is also elastic at the bottom and guides the liquid which forms the jet E. The rest of the phenomena and action are the same as in Fig. 1.

The distinguishing features of the present invention compared with those hitherto known are the strong mechanical shocks imparted to the jets escaping from the outlet opening. These shocks cause the jet to vi brate in accordance with, and with an amplitude in proportion to the sound and words to be transmitted. Moreover, the elasticity of a very small portion of the pipe guiding the liquid, gives the sounds reproduced a very great clearness.

After having briefly described the invention, the details of the apparatus will be now explained.

In order to make the liquid jet fall smoothly and in a closed steady column, for a certain distance, it is necessary that the outlet opening should have a considerably smaller diameter than the pipe. If this pipe were not subjected near the outlet opening to any breakage or the like, it would be sufficient if it had an inside diameter one and a half times as great as the diameter of the orifice. As, however, the hard material of the pipe must be broken or perforated near the outlet opening (as will be shown hereinafter), it is necessary to make the diameter of the pipe still greater. Good results are, for instance, obtained by making the inside diameter of the pipe three to four millimeters, and that of the orifice 1.5. These figures are, however, not binding, and can be modified if desired. Moreover, the thickness of the wall in which the orifice is made should be as small as possible, more particularly near the orifice.

Whatever be the modifications, the pipe must not be elastic throughout the whole of its length, as otherwise the vibrations would be transmitted to a great distance from the point where the diaphragm is secured, which follows from the inertia of the material (usually rubber)and would produce secondary vibrations of smaller frequency which would combine with those to be transmitted, and disturb them. The unpleasant result of that circumstance shows itself very clearly in telephonic lines of great length in which high pitched sounds are easily weakened, whereas low pitched sounds among which. the disturbing sounds are generally found, are transmitted with considerable intensity and sometimes make the speech completely unintelligible.

The various and chief among the methods for obtaining the elastic or the non-rigid connection between the diaphragm and the pipe D will now be described.

Figs. 3 to 13 show various constructions of the pipe D in connection with the vibrating diaphragm B.

Figs. 3 to 7 relate to the arrangement shown in Fig. 1, and-Figs. 8 to 13 to the modified construction shown in Fig. 2.

In Fig. 3 the diaphragm B is perforated in the center by the short pipe 0 (secured to the latter), and provided at the bottom with the outlet orifice. The inside diameter of the two pipes C and D is about the same, and the upper edge of (l is very near the bottom edge of D. The two pipes are connected by means of a short rubber tube 0 which, owing to its elasticity, enables the diaphragm to vibrate, without the pipe D participating in the vibration.

Fig. 4 differs from Fig. 3 by the position of the pipe C in which the outlet opening is at the top. Without coming in contact with the walls, the jet flows in the upper part of its course through its interior; this has the advantage of overcoming the drawback due to the existence of an excessive amount of liquid near the outlet opening, the opening thus remaining in the neighborhood of the elastic part of the pipe.

In Fig. 5, in order to reduce the mass of liquid in the neighborhood of the outlet opening to a still greater extent, the pipe D is also reduced at its bottom end, so that it has a diameter which is only slightly larger than, or even the same as that of the opening in C.

In Fig. 6 all rigid connection of the pipe with the diaphragm is avoided. The jet, coming from the outlet opening in the pipe D, flows through an opening made in the center of the diaphragm of approximately the same width, and can just touch its edges. The diaphragm can be made in one single piece or it may be provided in the center with a material suitable for erforation, such as glass, metal, etc. The pipe D is also not rigidly connected to the diaphragm B in Fig. 7, the diaphragm in this construction being perforated as in Fig. 6. The pipe D is here no longer reduced at the bottom end, or is reduced to a very small extent, but its lower edge is arranged very near the diaphragm. The liquid current divides into two portions, the central portion forms the jet and the rest flows in the shape of a fine liquid film over the diaphragm and is laterally discharged, without the acoustic vibrations of the diaphragm being affected by it.

Fig. 8 which, with those following refers to the modified construction shown in Fig. 2, is similar to Fig. 3. It differs from it only by the vertical diaphragm B acting, by means of a rigid body P, on the rubber part 0 connecting the pipes D and C.

In the same way Fig. 9 is similar to Fig. 4.

In Fig. 10, the two pi es D and C are replaced by a single pipe (5 provided with the outlet opening at the bottom. Laterally, and near the said outlet, it is provided with an opening R closed by an elastic diaphragm, such, for instance, as a piece of rubber tube drawn over the pipe. In this way, the opening R is closed, and the liquid cannot escape at that point. At the elastic wall closing the opening R is secured the support P of the diaphragm B.

In Fig. 11 a similar pipe Q is provided with a lateral opening closed by a piston S working with very little friction. As it is very difficult to obtain perfect closing without a great deal of friction, it is advisable to arrange a rubber tube T over the piston and. the out-turned edge of the opening. he piston is connected at its outer end to the diaphragm B, the vibrations of which are transmitted to the piston S, without the rubber part T constituting a great obstacle.

Figs. 12 and 13 have a pipe similar to the preceding Figs. 10 and 11. The opening of the pipe Q in the first case is closed by means of a conical valve or pin U, and in Fig. 13 by a flat valve V, which valves are caused to vibrate by the diaphragm B. The valves never come in actual contact with the pi )es, the result being a constant small loss of liquid, which, however, does not affect the formation of the main jet.

Many other devices could be described which, however, are sim ly variations of those described, and 'simpl y fulfil the object of making the vibrating diaphragm act on a small, sufficiently elastic or movable portion of the pipe guiding the liquid.

In each of the arrangements described the contractions of the jet approximately correspond to the sound waves striking the diaphragm, both as regards amplitude and frequency, and no other disturbing periods are noticeable, if the collector, which will be more fully described hereinafter, is not too far away from the outlet opening.

It is of great importance that the intensity of tele )honic currents should be as great as possib e, and to that end the collector must have its upper area as large as possible, and correspondingly the diameter of the outlet opening must not be too small. The shape of the collector shown in Fig. 1, is not the only one that may be used. In Fig. 14 the two conducting bodies of the collector are made of two circular rings F and G of platinum, or some other material that is a good conductor, and is not affected by the liquid. The continuity of the surface and the electrical insulation between F and G are obtained by two layers of an electrically insulating substance H, such as glass, procelain, enamel, vulcanized rubber, etc. The outer diameter of collectors of this kind can be even as large as several centimeters, and the pulsations of the thickness of the liquid film produced by the jet impinging against the center of the collector, always correspond exactly to the vibrations to be transmitted. The intensity of the electric current increases with the diameter of the rings of the collector and with their proximity to each other. If it be desired to increase it, a multiple collector, shown in Fig. 15, with three rings, can be used. The odd rings (first and third) marked F are in permanent electrical connection (not shown in the drawings) and form together one of the electrodes of the collector. The other electrode is represented by the central ring G. It is, besides, clear, that collectors can be made with a still greater number of rings, alternately connected together.

As already stated, in every construction according to this invention hereinbetore de scribed, the liquid jet is vertical, and this is certainly the most convenient arrangement, as the liquid film spreads in all directions on the collector in a uniform and symmetrical manner, but the vertical arrangement is not essential although it is desirable and preferable.

What I claim as my invention and desire to secure by Letters Patent is 1.. An electro dynamic microphone of the kind described comprising a vibratory diaphragm, a liquid supply tube and an elastic connection between the diaphragm and the outlet end of the liquid supply tube, in combination with an electrode consisting of an outer conducting ring and a central conducting rod of large diameter to readily transmit current of light intensity, and an intervening ring of non-conducting material the thickness of which is of the same dimensions as the liquid wave corresponding to the mean sound wave to be transmitted, substantially as set forth.

2. An electro dynamic microphone of the kind described comprising a vibratory diaphragm, a liquid supply tube and an elastically connected extension thereof, in combination with an electrode consisting of an outer conducting ring and a central conducting rod of large diameter to readily transmit current of light intensity, and an intervening ring of non-conducting material the thickness of which is of the same dimensions as the liquid wave corresponding to the mean sound wave to be transmitted substantially as set forth.

3. An electro dynamic microphone of the kind described comprising a vibratory diaphragm, a liquid supply tube, an extension elastically connected thereto and connected to the vibratory diaphragm, in combination with an electrode consisting of an outer con ducting ring and a central conducting rod of large diameter to readily transmit current of light intensity, and an intervening ring of nonconducting material the thickness of which is of the same dimensions as the liquid wave corresponding to the mean sound wave to be transmitted substantially as set forth.

4. An electro dynamic microphone of the kind described comprising a vibratory diaphragm, a liquid supply tube, an extension elastically connected thereto and connected to the vibratory diaphragm, in combination with an electrode consisting of an outer conducting ring and a central conducting rod of large diameter to readily transmit current of ligl'it intensity, and an intervening ring of non-conducting material the thickness of which is of the same dimensions as the liquid wave corresponding to the mean sound wave to be transmitted substantially as set forth.

5. An electro dynamic microphone of the kind described comprising a vibratory diaphragm, a liquid supply tube, an extension elastically connected thereto and connected to the vibratory diaphragm, the outlet orifice of the extension being relatively much smaller than that of the supply tube, in combination with an electrode consisting of an outer conducting ring and a central conducting rod of large diameter to readily transmit current of light intensity, and an intervening name to this specification in the presence of rifng (1)1fI110IL-(3Ondliftlng matierial the thickness two subscribing Witnesses. 0 W lOl is of t e same imensions as tie liquid wave corresponding to the mean sound QUIR 1N0 MAJORANA' 5 Wave to be transmitted substantially as set Witnesses:

forth. A. RAGGI,

In testimony whereof I have signed my EUs'rI SYUYND. 

